1. Technical Field
The disclosure relates to an electronics device, and more specifically relates to a transmitter and receiver in a DSL communication system capable of measuring crosstalk in a legacy communication line.
2. Related Art
In DSL (Digital Subscriber Line) communications, a transmitter and receiver communicate with one another over a plurality of “lines.” Each line includes a twisted pair of wires for communicating information. Each of the lines is typically loaded with different information so as to allow for parallel communication, and increased throughput.
Because the lines are loaded differently, the lines will interfere with one another in the form of crosstalk. The crosstalk may be generated by undesired capacitive, inductive, or conductive coupling between the lines, and will cause an undesired effect on the information being transmitted in those lines.
For example, data communicated in DSL is often transmitted as a QAM (Quadrature Amplitude Modulation) signal in which binary data is represented by an amplitude and phase corresponding to a particular location on a quadrature constellation. While being transmitted through particular line, the crosstalk generated in the line from the other lines may cause a shift in the amplitude and/or phase of the signal, thereby causing a receiver of the data to misread the binary data contained within the signal as corresponding to a different location of the quadrature constellation. In other words, crosstalk can cause bit errors in transmitted data or limit distance between two points of a constellation and therefore limit achievable signal-to-noise ratio (SNR).
The recent G.993.5 (G.vector) DSL standard includes a built-in crosstalk measurement procedure. However, legacy lines (e.g., lines following earlier DSL standards) lack this capability. Therefore, it is difficult to employ the G.vector crosstalk measurement procedure in the legacy line. One conventional method for measuring the crosstalk in the legacy line involved transmitting the OPV1 signal on the legacy line prior to a handshake procedure. However, when performed in this manner, prior to the handshake, the impedance seen by the legacy line may be different than that seen during showtime (e.g., data transmission) mode, which may lead to an incorrect calculation of crosstalk.
The disclosure will now be described with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the reference number.